Learn French: Certaines chaises sont dans l'autre salle.

In this sentence, Certaines is an indefinite adjective describing the noun chaises (chairs). Since chaise is feminine and there are multiple chairs, certaines must be in its feminine plural form to match. If we were talking about a masculine plural noun, like lits (beds), it would be Certains lits.

What is the difference between using Certaines and Quelques for "some"?

Both can translate to "some", but they have slightly different feels. Quelques focuses on a small quantity ("a few"). Certaines implies a specific but unnamed subset ("certain ones" out of a larger group). Here, Certaines chaises means "Certain chairs" are in the other room, contrasting them with the rest of the chairs.

How does the pronunciation of Certaines differ from the masculine Certains?

The masculine plural Certains ends with a nasal vowel sound. Because Certaines is feminine, that nasal sound disappears and the "n" is fully pronounced, making it sound like "ser-ten". The final "s" is silent in both forms.

Why use salle for "room" instead of pièce?